Insects, e.g. cockroaches, have found fascinating solutions for the problem of locomotion, in particular climbing over a large variety of obstacles. Neuroethological study has identified key behavioral patterns of these animals necessary for climbing: body flexion [1], center of mass (CoM) elevation [2], and local leg reflexes [3]. For example, when cockroaches start to climb over an obstacle they extend their middle legs to push the front body from the ground (CoM elevation). Afterwards, they tilt the prothorax down (i.e., body flexion) to support their locomotion and keep balance during climbing. In other situations, like locomotion through complex landscapes, there is a high probability for legs to get stuck. Searching and elevator reflexes tend to solve such problems leading to effective locomotion including climbing over obstacles.

Inspired by this finding, we develop reactive climbing control for our hexapod robot AMOS II. The controller is composed of three main neural circuits: neural locomotion control, neural reactive backbone joint control, and neural local leg reflex control. The locomotion control generates basic walking behavior including omnidirectional walking and different gaits of the robot. The reactive backbone joint control supports the climbing behavior of the robot by emulating the body flexion observed in cockroaches. The local leg reflex control activates searching and elevator reflexes as well as CoM elevation.

The controller was developed and successfully tested using our modular robot control environment, allowing physical simulation and simple transferring to AMOS II. Experimental results show that the developed reactive climbing control allows the robot to surmount obstacles with a maximum height of 13 cm which equals 75% of its leg length (see supplementary video at http://www.manoonpong.com/BCCN2012/ReactiveClimbing.wmv). As a comparison, a quadruped robot presented in [4] successfully negotiated obstacles up to 40% of its leg length while the hexapod Gregor I [5] and the octopod Scorpion IV [6] achieved a height of 65% and 55% of its leg length, respectively. In addition, AMOS II displays the three key behavior patterns found in neuroethological studies. Therefore, the experiments not only show that AMOS II exhibits outstanding climbing capabilities, but its control system also generates climbing behavior similar to the behavior observed in insects.